Salty food waste is difficult to manage with previous methods such as composting, anaerobic digestion, and incineration, due to the hindrance of salt and the additional burden to handle high concentrations of organic wastewater produced when raw materials are cleaned. This study presents a possibility of recycling food waste as fuel without the burden of treatment washing with water by pyrolyzing and scrubbing. For this purpose, salty food waste with 3% NaCl was made using 10 materials and pyrolysis was conducted at temperature range between 200–400 °C. The result was drawn from elementary analysis (EA), X-ray photoelectron spectroscopy (XPS) analysis, atomic absorption spectrophotometry (AAS) analysis, water quality analysis and calorific value analysis of char, washed char, and washing water. The result of the EA showed that NaCl in food waste could be volatilized at a low pyrolysis temperature of 200–300 °C and it could be concentrated and fixed in char at a high pyrolysis temperature of 300–400 °C. The XPS analysis result showed that NaCl existed in form of chloride. Through the Na content result of the AAS analysis, NaCl remaining in char after water scrubbing was determined to be less than 2%. As the pyrolysis temperature increased, the chemical oxygen demand (COD) value of scrubbing water decreased rapidly, but the total phosphorus and nitrogen contents decreased gradually. The cleaned pyrolysis char showed an increase of higher heating value (HHV) approximately 3667–9920 J/g due to the removal of salt from the char and, especially at 300–400 °C, showed a similar HHV with normal fossil fuels. In conclusion, salty food waste, which is pyrolyzed at a temperature of 300–400 °C and cleaned by water, can be utilized as high-energy refuse derived fuel (RDF), without adverse effects, due to the volatilization of Cl and an additional process of contaminated water.

In view of a water-energy-food (WEF) nexus strategy, the present work assessed the bioenergy production potential of Halimione portulacoides used for the phytoremediation of nutrient-rich simulated wastewater from saltwater-based integrated multi-trophic aquaculture (IMTA). Specimens of this halophyte plant were grown in hydroponics under four different nutrient treatments with distinct nitrogen (N) and phosphorous (P) concentrations. Ultimate and proximate analysis, calorific value and thermogravimetric analysis coupled to mass spectrometry were used to assess the bioenergy potential of the non-edible biomass of the plants, namely the canes (C) and roots (R), and of commercial pellets (CP), which were used as benchmark. R and, especially, CP had higher carbon but lower oxygen content and larger volatiles but lower ashes than C. The higher heating values (HHV) of C (16–17 MJ kg⁻¹) and R (17–18 MJ kg⁻¹) were the same order as those of conventional energy crops and CP (20 MJ kg⁻¹). Although mass loss and associated gaseous emissions during temperature programmed pyrolysis occurred mainly between 250 and 650 °C for all biomasses, they took place at slightly higher temperatures for C > CP > R. In any case, the integrated gaseous emissions during the pyrolysis of C, R, and CP were very similar and included H₂, CH₄, CO, and CO₂ (syngas main constituents). Biomass production of C was affected by the nutrients load of the applied treatments, but this was not the case for R. Also, the nutrients treatments had no detectable effects on the biomasses’ ultimate or proximate analysis, HHV, thermal decomposition or resultant gaseous emissions. Thermal properties and behaviour of C and R were very similar to those of CP, showing their potential for bioenergy production and revealing that a WEF nexus strategy can be implemented in IMTA by energetic valorization of non-edible biomass of H. portulacoides used for water phytoremediation.

Biochar is the product of the pyrolysis of organic materials in a reduced state. In recent years, biochar has received attention due to its applicability to organic waste management, thereby leading to active research on biochar. However, there have been few studies using food waste. In particular, the most significant difference between food waste and other organic waste is the high salinity of food waste. Therefore, in this paper, we compare the chemical characteristics of biochar produced using food waste containing low- and high-concentration salt and biochar flushed with water to remove the concentrated salt. In addition, we clarify the salt component behavior of biochar. Peak analysis of XRD confirms that it is difficult to find salt crystals in flushed char since salt remains in the form of crystals when salty food waste is pyrolyzed washed away after water flushing. In addition, the Cl content significantly decreased to 1–2% after flushing, similar to that of Cl content in the standard, non-salted food waste char. On the other hand, a significant amount of Na was found in pyrolyzed char even after flushing resulting from a phenomenon in which salt is dissolved in water while flushing and Na ions are adsorbed. FT-IR analysis showed that salt in waste affects the binding of aromatic carbons to compounds in the pyrolysis process. The NMR spectroscopy demonstrated that the aromatic carbon content, which indicates the stability of biochar, is not influenced by the salt content and increases with increasing pyrolysis temperature.